Virtual video on demand using multiple encrypted video segments

ABSTRACT

A method and apparatus for providing a virtual video on demand services is disclosed. The method and apparatus disclose the storing of a segment of the video program in advance for VOD viewing at a later time. When the subscriber selects VOD service, a pre-stored video segment is retrieved for presentation to the subscriber. Remaining video program segments simultaneously broadcast on a plurality of channels are recorded in parallel while the pre-stored video program segment is retrieved and presented to the user.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to systems and methods forproviding video program material to subscribers, and in particular to amethod and system for providing near video on demand services.

[0003] 2. Description of the Related Art

[0004] In recent years, there has been increasing interest in providingvideo-on-demand (VOD) services to cable and satellite televisionsubscribers. With an idealized VOD system, the user simply selects thedesired program material (video or audio), transmits the selection tothe video provider, and the video program is transmitted to the user ina real time data stream. With such idealized systems, the user cancontrol the display of the video program in real time by issuing stop,rewind, fast-forward, or pause commands. These commands are received bythe video server, and the data stream is interrupted or modified asappropriate for the command from the viewer. Essentially, this VODparadigm implements a client-server architecture wherein the user's settop box (or computer) is the client, and the video server is the server.

[0005] While the foregoing VOD system would provide the user withbeneficial and flexible service, it suffers from several majordisadvantages. First, it places tremendous difficulties on theinput/output (I/O) multiplexing and bandwidth capabilities of the videoserver. While the real-time transmission of a single video program to asingle video subscriber is relatively easy to accomplish, this is notthe case when a wide variety of different video sources may be requestedby a large number of video subscribers all at the same time.Essentially, because subscriber requests are generally asynchronous,each request for a particular video program requires a separatetransmission, and each separate transmission consumes a portion of theavailable bandwidth.

[0006] Second, the foregoing systems are intolerant of communicationlatencies between the user and the video server. Particularly whenfast-forwarding and rewinding through video sequences to look forsegments of interest, users may issue a number of commands in rapidsuccession, expecting near instantaneous responses from the videoserver. Even minor communication latencies can become an extremeirritation to the user.

[0007] Many different solutions to these problems have been proposed,but for the most part, these solutions have had limited success. For themost part, these solutions are unnecessarily complicated and expensivebecause they focus on streamlining the data transmission process withthe use of higher capability equipment, or a plurality of remotelylocated video servers.

[0008] What is needed is a method for supplying video on demand to alarge number of subscribers, each of which may request a differentprogram and at times asynchronous to one another. The present inventionsatisfies that need.

SUMMARY OF THE INVENTION

[0009] In summary, the present invention describes a system and methodin which an integrated receiver/decoder (IRD) or similar device is usedto select and store programs to support video on demand. In oneembodiment, programs are selected by use of a broadcaster-controlledattribute, such as a flag in a program guide. In another embodiment,this is accomplished by a customer setup profile (e.g. programs withDOLBY digital or programs of a specific genre). The IRD scans theprogram guide to identify VOD candidates, and based on the start timesin the program guides and transport streams, the schedules thepre-recording of segments of the identified programs.

[0010] The scheduled pre-recording of segments of the identifiedprograms can occur at a rate that is faster than real time. Toaccomplish this, the IRD scans the program guide and learns the starttime for each of the NVOD candidates. When multiple staggered programstart times are found, the IRD determines which portions of the programcan be received and stored in parallel in order to pre-record allrelevant program segments in the shortest time. IRDs with single tunersacquire staggered start times that are on the same transport stream,while multi-tuner IRDs can collect data from many transport streams.After the storage process is complete, the customer is informed (forexample, by the program guide), that the video program is available forVOD playback.

[0011] Once the user demands VOD playback, the pre-stored video segmentis played back to the user, while the remaining subsequent segments ofthe video program are received and recorded in parallel. Thesesubsequent segments are spliced to the pre-stored segment and to eachother to give the appearance of VOD playback. In one embodiment, the IRDacquires and stores a purchase information packet (PIP) for each programsegment. Further, where program is stored as multiple segments, MPEGdata embedded in the SMPTE time code or the presentation time stampinformation allows the IRD to perform MPEG on line editing to reassemblethe program into a single filestream. The timecode information alsoallows the IRD to acquire and store a video program withoutinterruption. The SMPTE timecode also allows the IRD to store a videoprogram with user interruptions. When the IRD is in the process ofstoring video information to a disk and the customer uses the IRD toview a different program, the IRD can later resume acquisition using alater rebroadcast of the same program to resume the storage at the pointbefore it was interrupted by the user.

[0012] In one embodiment, the time-staggered versions of selected (e.g.PPV) video programs are transmitted on channels that are broadcast on acommon transponder. This allows a single-tuner IRD to acquire and storeseveral program segments in parallel, resulting in faster than real timestorage of the subsequent segments of video program while the customeris viewing the pre-stored program segment. So configured, the IRD canreceive and store a video program 2-5 times faster than real time. Thisallows the user to fast-forward anywhere in the program within a singlerebroadcast interval.

[0013] Decryption of the pre-stored program segments and the subsequentprogram segments is also be performed by the IRD. Since program segmentsare pre-stored by the IRD in anticipation of customer demand and thestorage of the pre-stored segments may be autonomously performed by theIRD, the broadcaster may not be aware of which program segments werestored by each customer's IRD. In one embodiment, the IRD solves thisproblem by storing conditional access information such as a purchaseinformation parcel (PIP) with each stored program segment. When the usermakes a VOD demand, a message is sent from the IRD identifying each ofthe subsequent segments of the video program. In response, the IRDreceives the PIPs corresponding to the subsequent program segments, anddecodes, and splices them together as required. To prevent the customerfrom being billed for multiple viewing of the same program, a modifiedbilling system recognizes that the program segments sent to thecustomer's IRD were part of a VOD program, and would bill the customerfor a single viewing of all of the video segments. In one embodiment,separate PIPs for VOD service are defined, each of which having a valuewhich is an appropriate (e.g. pro-rated according to the time length ofthe segment) fraction of the total charge for the complete programdefined. In another embodiment, the billing system recognizes the PIPsas associated with program segments which were broadcast simultaneously,and adjusts the bill for a single viewing accordingly.

[0014] One embodiment of the present invention is described as a methodcomprising the steps of selecting at least one of a plurality of videoprograms for VOD service; receiving and storing a first segment of theselected video program in a local storage device before accepting a userdemand to view the selected video program, wherein the temporal lengthof the first segment is at least substantially equivalent to aretransmission interval; and, after accepting the user demand to viewthe selected video program, retrieving the stored first segment forpresentation while receiving and storing subsequent segments of thevideo program from each of the plurality of channels transmitting aportion of the selected video program in parallel.

[0015] One embodiment of the present invention is described by a methodof storing or viewing a video program in response to a user demand,wherein the video program is repeatedly transmitted on one of aplurality of channels, each repeated transmission separated in time froma preceding transmission of the video program by a retransmissioninterval and being transmitted on a different channel than the previoustransmission. The method comprises the steps of selecting at least oneof a plurality of video programs, and receiving a plurality of timesegments of the selected video program in parallel, wherein each of thetime segments is received on a different one of the channels.

[0016] Another embodiment of the present invention is described by anapparatus comprising an input device for accepting a selection of atleast one of a plurality of video programs for VOD service; a tuner forreceiving multiple segments of the selected video program in parallel,wherein each segment is received on one of a plurality of channels; anda storage device, for pre-storing a first segment of the selected videoprogram and for storing subsequent segments of the selected videoprogram in parallel while retrieving the pre-stored first segment of theselected video program.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0018]FIG. 1 is a diagram showing an overview of a video distributionsystem;

[0019]FIG. 2 is a block diagram of an integrated receiver/decoder forpracticing the present invention;

[0020]FIG. 3 is a block diagram showing a typical uplink configurationshowing how video program material is uplinked to a satellite fortransmission to subscribers using a single transponder;

[0021]FIG. 4A is a diagram of a representative data stream received froma satellite;

[0022]FIG. 4B is a diagram illustrating the structure of a data packet;

[0023]FIG. 5 is a block diagram illustrating transport module functions;

[0024]FIG. 6 is a diagram illustrating the transmission of a videoprogram to provide near video on demand (NVOD) service;

[0025]FIGS. 7A and 7B are flow charts presenting exemplary method stepsused to practice one embodiment of the present invention;

[0026]FIG. 8A is a diagram illustrating aspects of the operation of thepresent invention;

[0027]FIG. 8B is a diagram showing additional detail regarding thesplicing of program material;

[0028]FIG. 8C is a diagram showing additional detail regarding cachingof program material;

[0029]FIG. 9 is a flow chart illustrating exemplary operations used toselect at least one of the plurality of video programs for VOD service;and

[0030]FIG. 10 is a diagram illustrating exemplary operations used toselect one of the plurality of video programs for VOD service in anotherembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] In the following description, reference is made to theaccompanying drawings which form a part hereof, and which-show, by wayof illustration, several embodiments of the present invention. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.

[0032]FIG. 1 is a diagram illustrating an overview of a videodistribution system 100. The video distribution system 100 comprises acontrol center 102 in communication with an uplink center 104 via aground link 114 and with a subscriber 110 via a public switchedtelephone network (PSTN) or other link 120. The control center 102provides program material to the uplink center 104, coordinates with thesubscribers 110 to offer pay-per-view (PPV) program services, includingbilling and associated decryption of video programs.

[0033] The uplink center receives program material and program controlinformation from the control center 102, and using an uplink antenna106, transmits the program material and program control information tothe satellite 108. The satellite receives and processes thisinformation, and transmits the video programs and control information tothe subscriber via downlink 118. The subscriber 110 receives thisinformation using the subscriber antenna 112.

[0034] In one embodiment, the subscriber antenna 112 is an 18-inchslightly oval-shaped Ku-band antenna. The slight oval shape is due tothe 22.5 degree offset feed of the LNB (low noise block converter) whichis used to receive signals reflected from the subscriber antenna 112.The offset feed positions the LNB out of the way so it does not blockany surface area of the antenna 112 minimizing attenuation of theincoming microwave signal.

[0035] The video distribution system 100 can comprise a plurality ofsatellites 108 in order to provide wider terrestrial coverage, toprovide additional channels, or to provide additional bandwidth perchannel. In one embodiment of the invention, each satellite comprises 16transponders to receive and transmit program material and other controldata from the uplink center 104 and provide it to the subscribers 110.However, using data compression and multiplexing techniques the channelcapabilities are far greater. For example, two-satellites 108 workingtogether can receive and broadcast over 150 conventional (non-HDTV)audio and video channels via 32 transponders.

[0036] While the invention disclosed herein will be described withreference to a satellite based video distribution system 100, thepresent invention may also be practiced with terrestrial-basedtransmission of program information, whether by broadcasting means,cable, or other means. Further, the different functions collectivelyallocated among the control center 102 and the uplink center 104 asdescribed above can be reallocated as desired without departing from theintended scope of the present invention.

[0037] Although the foregoing has been described with respect to anembodiment in which the program material delivered to the subscriber isvideo (and audio) program material such as a movie, the foregoing methodcan be used to deliver program material comprising purely audioinformation as well.

[0038]FIG. 2 is a block diagram of an integrated receiver/decoder (IRD)200 (also hereinafter alternatively referred to as receiver 200). Thereceiver 200 comprises a tuner/demodulator 204 communicatively coupledto the LNB 202. The LNB 202 converts the 12.2- to 12.7 GHz downlink 118signal from the satellites 108 to, e.g., a 950-1450 MHz signal requiredby the receiver's 200 tuner/demodulator 204. The LNB 202 may provideeither a dual or a single output. The single-output LNB 202 has only oneRF connector, while the dual output LNB 202 has two RF output connectorsand can be used to feed a second receiver or some other form ofdistribution system.

[0039] The tuner/demodulator 204 isolates a single, digitally modulated24 MHz transponder, and converts the modulated data to a digital datastream. The digital data stream is then supplied to a forward errorcorrection (FEC) decoder 206. This allows the receiver 200 to reassemblethe data transmitted by the uplink center 104 (which applied the forwarderror correction to the desired signal before transmission to thesubscriber 110) verify that the correct data signal was received, andcorrect errors, if any. The error-corrected data may be fed from the FECdecoder module 206 to the transport module via an 8-bit parallelinterface.

[0040] The transport module 208 performs many of the data processingfunctions performed by the receiver 200. The transport module 208processes data received from the FEC decoder module 206 and provides theprocessed data to the video MPEG decoder 214 and the audio MPEG decoder216. In one embodiment of the present invention, the transport module,video MPEG decoder and audio MPEG decoder are all implemented onintegrated circuits. This design promotes both space and powerefficiency, and increases the security of the functions performed withinthe transport module 208. The transport module 208 also provides apassage for communications between the microcontroller 210 and the videoand audio MPEG decoders 214, 216. As set forth more fully hereinafter,the transport module also works with the access card 212 to determinewhether the subscriber 110 is permitted to access certain programmaterial. Data from the transport module can also be supplied toexternal communication module 226. The operations performed by thetransport module are further illustrated and described with respect toFIG. 3.

[0041] The access card 212 functions in association with other elementsto decode an encrypted signal from the transport module 208. The accesscard 212 may also be used for tracking and billing these services. Inone embodiment of the present invention, the access card is a smartcard, having contacts cooperatively interacting with contacts in thereceiver 200 to pass information. In order to implement the processingperformed in the access card 212, the receiver 200, and specifically thetransport module 208 provides a clock signal to the access card 212.

[0042] Video data is processed by the MPEG video decoder 214. Using thevideo random access memory (RAM) 236, the MPEG video decoder 214 decodesthe compressed video data and sends it to an encoder or video processor216, which converts the digital video information received from thevideo MPEG module 214 into an output signal usable by a display or otheroutput device. By way of example, processor 216 may comprise a NationalTV Standards Committee (NTSC) or Advanced Television Systems Committee(ATSC) encoder. In one embodiment of the invention both S-Video andordinary video (NTSC or ATSC) signals are provided. Other outputs mayalso be utilized, and are advantageous if ATSC high definitionprogramming is processed.

[0043] Audio data is likewise decoded by the MPEG audio decoder 216. Thedecoded audio data may then be sent to a digital to analog (D/A)converter 218. In one embodiment of the present invention, the D/Aconverter 218 is a dual D/A converter, one for the right and leftchannels. If desired, additional channels can be added for use insurround sound processing or secondary audio programs (SAPs). In oneembodiment of the invention, the dual D/A converter 218 itself separatesthe left and right channel information, as well as any additionalchannel information. Other audio formats may similarly be supported. Forexample multi-channel digital audio formats, such as DOLBY DIGITAL AC-3.

[0044] A description of the processes performed in the encoding anddecoding of video streams, particularly with respect to MPEG and JPEGencoding/decoding, can be found in Chapter 8 of “Digital TelevisionFundamentals, by Michael Robin and Michel Poulin, McGraw-Hill, 1998,which is hereby incorporated by reference herein.

[0045] Microcontroller 210 receives and processes command signals fromthe remote control 224, a receiver 200 keyboard interface, and/oranother input device. The microcontroller receives commands forperforming its operations from a processor programming memory, whichpermanently stores such instructions for performing such commands. Theprocessor programming memory may comprise a read only memory (ROM) 238,an electrically erasable programmable read only memory (EEPROM) or,similar memory device. The microcontroller 210 also controls the otherdigital devices of the receiver 200 via address and data lines (denoted“A” and “D” respectively, in FIG. 2).

[0046] The modem 240 connects to the customer's phone line via the PSTNport 120. It calls e.g. the program provider and transmits thecustomer's program purchases for billing purposes, and/or otherinformation. The modem 240 is controlled by the microprocessor 210. Themodem 240 can output data to other I/O port types including standardparallel and serial computer I/O ports.

[0047] The present invention also comprises a local storage unit such asthe video storage device 232 for storing video and/or audio dataobtained from the transport module 208. Video storage device 232 can bea hard disk drive, a read/writable compact disc of DVD, a solid stateRAM, or any other storage medium. In one embodiment of the presentinvention, the video storage device 232 is a hard disk drive withspecialized parallel read/write capability so that data may be read fromthe video storage device 232 and written to the device 232 at the sametime. To accomplish this feat, additional buffer memory accessible bythe video storage 232 or its controller may be used. Optionally, a videostorage processor 230 can be used to manage the storage and retrieval ofthe video data from the video storage device 232. The video storageprocessor 230 may also comprise memory for buffering data passing intoand out of the video storage device 232. Alternatively or in combinationwith the foregoing, a plurality of video storage devices 232 can beused. Also alternatively or in combination with the foregoing, themicrocontroller 210 can also perform the operations required to storeand or retrieve video and other data in the video storage device 232.

[0048] The video processing module 216 output can be directly suppliedas a video output to a viewing device such as a video or computermonitor. In addition the video and/or audio outputs can be supplied toan RF modulator 234 to produce an RF output and/or 8 vestigal side band(VSB) suitable as an input signal to a conventional television tuner.This allows the receiver 200 to operate with televisions without a videooutput.

[0049] Each of the satellites 108 comprises a transponder, which acceptsprogram information from the uplink center 104, and relays thisinformation to the subscriber 110. Known multiplexing techniques areused so that multiple channels can be provided to the user. Thesemultiplexing techniques include, by way of example, various statisticalor other time domain multiplexing techniques and polarizationmultiplexing. In one embodiment of the invention, a single transponderoperating at a single frequency band carries a plurality of channelsidentified by respective service channel identification (SCID).

[0050] Preferably, the receiver 200 also receives and stores a programguide in a memory available to the microcontroller 210. Typically, theprogram guide is received in one or more data packets in the data streamfrom the satellite 108. The program guide can be accessed and searchedby the execution of suitable operation steps implemented by themicrocontroller 210 and stored in the processor ROM 238. The programguide may include data to map the channel numbers to satellitetransponders and service channel identifications (SCIDs), and alsoprovide TV program listing information to the subscriber identifyingprogram events.

[0051]FIG. 3 is a block diagram showing a typical uplink configurationfor a single satellite 108 transponder, showing how video programmaterial is uplinked to the satellite 108 by the control center 102 andthe uplink center 104. FIG. 3 shows three video channels (which could beaugmented respectively with one or more audio channels for high fidelitymusic, soundtrack information, or a secondary audio program fortransmitting foreign languages), and a data channel from a computer datasource 306.

[0052] The video channels are provided by a program source of videomaterial 300A-300C (collectively referred to hereinafter as videosource(s) 300). The data from each video program source 300 is providedto an encoder 302A-302C (collectively referred to hereinafter asencoder(s) 302). Each of the encoders accepts a program time stamp (PTS)from the controller 316. The PTS is a wrap-around binary time stamp thatis used to assure that the video information is properly synchronizedwith the audio information after encoding and decoding. A PTS time stampis sent with each I-frame of the MPEG encoded data.

[0053] In one embodiment of the present invention, each encoder 302 is asecond generation Motion Picture Experts Group (MPEG-2) encoder, butother decoders implementing other coding techniques can be used as well.The data channel can be subjected to a similar compression scheme by anencoder (not shown), but such compression is usually either unnecessary,or performed by computer programs in the computer data source (forexample, photographic data is typically compressed into *.TIF files or*.JPG files before transmission). After encoding by the encoders 302,the signals are converted into data packets by a packetizer 304A-304F(collectively referred to hereinafter as packetizer(s) 304) associatedwith each source 300.

[0054] The data packets are assembled using a reference from the systemclock 314 (SCR), and from the conditional access manager 308, whichprovides the SCID to the packetizers 304 for use in generating the datapackets. These data packets are then multiplexed into serial data andtransmitted.

[0055]FIG. 4A is a diagram of a representative data stream. The firstpacket segment 402 comprises information from video channel 1 (datacoming from, for example, the first video program source 300A). The nextpacket segment 404 comprises computer data information that wasobtained, for example from the computer data source 306. The next packetsegment 406 comprises information from video channel 5 (from one of thevideo program sources 300), and the next packet segment includesinformation from video channel 1 (again, coming from the first videoprogram source 300A). The data stream therefore comprises a series ofpackets from any one of the data sources in an order determined by thecontroller 316. The data stream is encrypted by the encryption module318, modulated by the modulator 320 (typically using a QPSK modulationscheme), and provided to the transmitter 322, which broadcasts themodulated data stream on a frequency bandwidth to the satellite via theantenna 106. The receiver 200 receives these signals, and using theSCID, reassembles the packets to regenerate the program material foreach of the channels. As shown in FIG. 4A, null packets created by thenull packet module 312 may be inserted into the data stream as desired.

[0056]FIG. 4B is a diagram of a data packet. Each data packet (e.g.402-416) is 147 bytes long, and comprises a number of packet segments.The first packet segment 420 comprises two bytes of informationcontaining the SCID and flags. The SCID is a unique 12-bit number thatuniquely identifies the data packet's data channel. The flags include 4bits that are used to control whether the packet is encrypted, and whatkey must be used to decrypt the packet. The second packet segment 422 ismade up of a 4-bit packet type indicator and a 4-bit continuity counter.The packet type identifies the packet as one of the four data types(video, audio, data, or null). When combined with the SCID, the packettype determines how the data packet will be used. The continuity counterincrements once for each packet type and SCID. The next packet segment424 comprises 127 bytes of payload data, which is a portion of the videoprogram provided by the video program source 300. The final packetsegment 426 is data required to perform forward error correction.

[0057]FIG. 5 is a block diagram showing additional detail regarding theoperations of the transport module. The data packets which are received,demodulated, synchronized and reverse FEC coded from the FEC module 206are provided to a demultiplexer such as the SCID select module 502.Program selection information is processed by the microcontroller 210,and used to select the one or more SCIDs associated with the desiredprogram (a program may be separated into several streams, each with anassociated SCID). As set forth more fully herein, program selection caninclude a selection for ordinary viewing, or for VOD recording. Inaddition, the selection of a program for VOD recording can beaccomplished by the subscriber, according to an express selection, aresult of a processing routine to predict the subscribers preferencesfrom a viewing history, or by selection by the control center 102.

[0058] The SCID select module compares the selected SCID or SCIDs withthe SCIDs for the incoming packets, and passes those packets with SCIDsmatching the selected channel(s). For single channel service,non-selected packets (packets without the subscriber-selected SCID) aresimply discarded.

[0059] In the typical case where a video program comprises multiplestream elements, the SCID select module passes the required packets. Ifmore than one channel is desired (e.g. to allow the reception andrecording multiple channels at a time while simultaneously viewing them)the SCID select module 502 passes these the stream elements for theadditional channels as well.

[0060] In the preferred embodiment, all program material is encrypted.For viewing encrypted programming, the receiver 200 is responsible forverifying that access should be granted, and if so, decrypting the datapackets so the program material can be viewed by the subscriber. Forunencrypted programming, the data router 514 directs the data packetsdirectly in the system RAM 228 via DMA 508.

[0061] To provide program information for use in the distribution andviewing of PPV program material, the control center 102 transmits (viathe uplink center 104 and the satellite 108) a purchase informationpacket (PIP) that is associated with PPV program materials described inthe program information guide. When the subscriber wants to view PPVprogram material, the receiver 200 is used to select the correspondingPPV program material. The receiver obtains a PIP pointer, and tunes to atransponder that carries the PIP. A PIP pointer is a numerical valuethat is stored with a program in the program guide stream orfunctionally computed from a program's channel and start time (e.g. PIPpointer=program.PIP_pointer, or PIP pointer=f(channel, start time)). ThePIP is received by the receiver 200 by acquiring the PIP for the sendPIP pointer, and provided to the access card 212, which checks the PIPfor purchasability (e.g. blackouts, rating, credit balance, etc.).

[0062] Each data packet is associated with a control word packet (CWP)that is received by the transport module 208. The CWP encodes eachprogram to prevent tampering, and is used to generate a CW and a CWstatus, which are stored in the CW memory 504. The CW is used to enabledata packets to be retrieved from the system RAM 228 and provided to thevideo MPEG decoder 214 and/or audio MPEG decoder 216, and may also beused to decrypt the data packet itself

[0063] As set forth more fully below, the present invention alsoprovides non-real time viewing capability to the viewer. This non-realtime viewing capability includes (1) the ability to store a videoprogram in its entirety for complete off-line viewing at a later date,and (2) the ability to “pre-store” the first portion of a video programto provide virtual VOD service. In case (2), an initial segment of thevideo program is recorded in advance of the user request (e.g., thefirst 30 minutes). When the user decides to view the video program, the“pre-stored” segment is played back, while the subsequent remainingvideo program segments (which are each transmitted on differentchannels) are recorded. These segments are spliced together to provide avirtual video on demand system that provides the appearance of truevideo on demand.

[0064] Programs eligible for VOD service may be indicated as such by theVOD indicator or other appropriate flag in the program guide or otherdata service. Eligibility may also be determined by analysis of theavailability alternate program information start times and determiningif the alternate program start times will support VOD service. In oneembodiment, the IRD determines VOD service availability using staggeredshowings of the same program by use of information in the program guide.The program guide supplies the channel number and start time of allprogram material. The IRD can use the staggered showing information torecord the program material at a rate faster than real time.

[0065] Programs that are eligible for VOD service may include encryptedPPV programs, encrypted non-PPV programs, and non-encrypted programs.

[0066] The storage of non-encrypted data segments is accomplished bypassing the data through the system RAM 228 (indicated by the firstswitch 514 in the up position) and then to the video storage device 232,or by passing the data directly from the transport module 208.

[0067] The retrieval of non-encrypted data segments is accomplished byreading the data segments from the video storage device 232 and routingthose data segments to the system RAM 228 using the data router 514 andthe DMA to system RAM 508, where they can be read and provided to theMPEG decoders 214, 216.

[0068] The storage of encrypted data packets can be accomplished in oneof two ways. First, the encrypted data packets can be decrypted by thedecryption module 506 as described above, and passed through the systemRAM 228 to the video storage device 232. This method is appropriate, forexample, when the subscriber 110 is entitled to view all encryptedprogram material (e.g. a monthly subscription). Alternatively, thereceiver 200 can store the data packets in encrypted form and decryptthem for later viewing after a purchase choice is made by the customer.In one embodiment data router 514 directs encrypted data segmentsdirectly to the video storage device 232. In another embodiment, theencrypted data is sent to the video storage device 232 via the systemRAM 228.

[0069] Two levels of encryption can also be used to implement anadditional layer of access control for PPV programs. A first level ofaccess control can be used to limit access to persons who are authorizedto purchase a PPV program (e.g. subscribers) and the second level ofaccess control can be used to limit access to the PPV program to thosewho have actually purchased a PPV program. In this case, data packetsmay be decrypted to the first level of access, and stored in the videostorage device 232. However, since the data packets are encryptedaccording to two levels of access control, the data must be read fromthe video storage device 232 and decrypted to the second level of accessbefore the video data can be decoded and presented to the user.

[0070] In either case, the encrypted data packets must be decryptedbefore presentation to the user. This is accomplished by reading theencrypted data packets from the video storage device 232, and routingthese packets to the decrypt module 506. These encrypted data packetsare then decrypted and stored in the system RAM 228 for DMA access bythe MPEG decoders 214, 216.

[0071] In one embodiment, the decryption process is accomplished asfollows. In response to a user demand and while retrieving the storedfirst segment 804 for presentation to the user, a message is transmittedto the IRD 200 separately identifying each of the subsequent segments806 of the selected video program and the user to the program sourcesuch as the control center 102 or the uplink center 104. A code or keysuch as the PIP is then received by the IRD 200. The key is later usedto decrypt the encrypted segments so the video program can be viewed bythe user.

[0072] In another embodiment, a message is transmitted to the IRD 200separately identifying each of the subsequent segments 806 of theselected video program and the user to the program source such as thecontrol center 102 or the uplink center 104. In response, a plurality ofcodes or keys are transmitted and received by the IRD 200, and each ofthe keys is used to decrypt an associated one of the encryptedsubsequent segments 806.

[0073]FIG. 6 is a diagram illustrating the transmission of a videoprogram to provide near video on demand (NVOD service). NVOD service isaccomplished by broadcasting the same video program 602 on a pluralityof program channels with each channel temporally separated by arebroadcast interval 604. As shown in FIG. 6, the video program can bebroadcast at 5:00 on channel 1 (using the appropriate SCID), 5:30 onchannel 2, 6:30 on channel 3, and so on. Using this broadcast technique,the video program can be viewed from the beginning to the end, withoutrequiring the user to wait for more than 30 minutes (hence, providingnear video on demand). As shown in FIG. 6, this means that at anyparticular time, during an time interval 606, different time segments ofthe video program 608A-608E (hereinafter referred to collectively assegments 608) are broadcast in parallel, and can be received by thereceiver 200.

[0074]FIGS. 7A and 7B describe a flow chart presenting exemplary methodsteps used to practice one embodiment of the present invention. First,as shown in FIG. 7A, at least one of a plurality of video programs isselected 702 for video service. The point in time at which the pluralityof video programs was selected for VOD service is indicated as t_(s)802. A first segment of the selected video program is then received andstored. This is illustrated in block 704 of FIG. 7A and by the“pre-store” interval 804 extending from time t_(p1) to time t_(p2) inFIG. 8A. Typically, the time length of the pre-stored video programmaterial segment 804 is equal to the rebroadcast interval t_(R) 604.This allows all of the subsequent time segments 806A-806D (collectivelyreferred to hereinafter as subsequent time segment(s) 806) of the videoprogram to be recorded while the pre-stored video program segment 804 isplayed back for viewing. However, the length of the pre-stored videoprogram material segment can be greater than the rebroadcast interval604, to provide additional video program material for use in splicingthe subsequent segments 806 to the pre-stored segment 804, or to provideadditional time for the splicing process to be completed.

[0075] Returning to FIG. 7A, when the user requests 706 VOD service, thepre-stored segment 804 is retrieved for presentation to the subscriber110. While this retrieval is taking place, the subsequent segments 806of the video program material are being received from some of theplurality of channels (channels 3, 4, 5, and 6 in FIG. 8A, for example)are received and stored in the video storage device 232. The foregoingoperations occur in parallel so that the data from all of the relevantchannels can be received and stored while retrieving the stored firstsegment for presentation to the subscriber 110. If necessary, this canbe implemented with separate disk drives or memories for fasterprocessing.

[0076] As shown in FIG. 8A, depending on the time the subscriber demandsVOD service t_(D), data present on some of the channels need not berecorded. For example, given the demand time t_(D) shown in FIG. 8A, thefirst portion of the program information on channel 6 need not berecorded, since it is duplicative of the information in the pre-storedsegment 804 being retrieved from the storage device 232. Instead, theonly program information that must be recorded is the lastt_(R)−(t_(D)−t_(A)) portion of the video segment, wherein t_(A) is thecommencement time for the most recent broadcast of the program, andt_(R) is the rebroadcast interval. The interval of the subsequent videoprogram segment 806D that must be recorded is shown as interval 808. Theremainder of the interval of the subsequent video program segment 806need not be recorded, and the bandwidth normally used for receiving andstoring this information can be directed to other purposes (e.g. storingother program material for VOD service).

[0077] Turning to FIG. 7B, the subsequent segments 806 are spliced tothe pre-stored segment 804 using the techniques set forth herein. In oneembodiment, the splicing of segments is prioritized according to pointin the video program currently selected by the user. If the user isviewing the video program from start to end, without interruption, fastforward, or rewind, the end of the pre-stored segment 804 is spliced tothe beginning of subsequent segment 806D first, and then the beginningof each subsequent segment is spliced to the end of the precedingsubsequent segment (hence, after splicing, the order of the segments ispre-stored segment 804, subsequent segment 806D, subsequent segment806C, etc.).

[0078] In one embodiment of the present invention, the user cannot fastforward past the pre-cached segment 804 until the immediately followingsegment (i.e. segment 806D) has been recorded. Hence, the VOD systemallows an asynchronous start of viewing, but truly random access to allprogram material is only available after all of the program segments806A-806D have been recorded.

[0079] However, since the multi-channel reception and storage describedherein permits the remainder of the program material to be downloadedrapidly, another embodiment of the present invention permits thesubscriber 110 to fast forward and rewind while viewing the retrievedpre-stored segment 804 and storing the subsequent segments 806. In suchcases, different splicing techniques are implemented. For example, ifthe user is in the middle of viewing the pre-stored segment 804 andissues a command to fast forward the program to a time near thebeginning of the last subsequent segment of the program 806A, thesplicing of subsequent segment 806B to subsequent segment 806A will begranted a higher priority than the splicing of pre-stored segment 804 tothe first subsequent segment 806D. It should also be noted that tofurther improve performance, data from the end of the pre-stored segment804 may be retrieved in parallel with other data being retrieved fromthe pre-stored segment 804 for subscriber viewing to allow essentially“pre-splice” the end of the pre-stored segment 804 to the beginning ofthe (recently received) subsequent segment 806D.

[0080] It should also be noted that the splicing between the pre-storedsegment 804 the first subsequent segment 806D can be performed atdifferent times, which can be advantageously chosen to minimize thesplicing time or to maximize fast-forward and rewinding capability.

[0081]FIG. 8B is a diagram illustrating the different times that thepre-stored segment 804 may be spliced to the first subsequent segment806D. By inspection, the first time at which a splice may be performedbetween pre-stored segment 804 and the subsequent segment 806D is a timet_(SP1), and the last time a splice may be performed is at time t_(SP2).The actual splicing time can be determined according to a number of userinput or program parameters. For example, the selection of a splice timeof t_(SP2) permits the user to fast-forward, reverse, and pause anywherewithin the pre-stored segment 804 at will with minimum programinterruption. Conversely, the selection of splice time t_(SP2) minimizesmemory requirements, as less program material need be stored to provideVOD service. Conversely, if the splice time t_(SP1) is selected, segment806D need not be stored at all, as the pre-stored segment 804 may bespliced to the broadcast program material as soon as practicable. Thiseffectively minimizes memory and throughput requirements. Further, iftime segment information is provided in the program material, fastforward and reverse operations may be implemented by splicing back topre-stored segment 804 program material as required.

[0082]FIG. 8C is a diagram showing additional detail regarding thecaching and splicing of program material. In the illustrated case, aprogram “A” is 125 minutes long, and the rebroadcast interval is 125minutes. Hence, the program includes four thirty-minute segments810B-8110E and a five-minute segment 810A. The IRD 200 pre-stores afirst segment 804 having 30 minutes of program material in anticipationof a customer's desire to view program “A.” This can occur, for examplein the interval between 6:30 and 7:00 as depicted in FIG. 8A. The PIP isalso pre-stored or cached if the program is a PPV program. Audio trackscan be recorded along with the video information. These audio tracks caninclude all audio tracks, or only one or more preferred audio tracks(i.e. audio tracks corresponding to a particular language or programrating).

[0083] After the customer requests viewing of the program material attime t_(D), the IRD 200 begins playing back the pre-recorded segment804, and searches the program guide for staggered showings of program“A”. The IRD 200 then begins to record the available program segments810A-810D from the staggered showings of program “A” while playing backthe prerecorded segment 804. After an amount of time elapses, a viewedportion 812 t_(V) of the pre-recorded segment 804 has been played backand portions 814A-814D of the remaining segments 810A-810D are recorded.As time passes, the viewed portion 812 t_(V) gets larger, as do therecorded portions 814A-814D or the remaining segments 810A-810D. Forexample, in the fourth illustration from the top of FIG. 8C, twenty-nineminutes of the prerecorded interval 812 have been played back, with 1minute of anticipated pre-recorded storage material 820 remaining, andthe IRD has completed caching 29 minutes of each 30 minute programsegment, as illustrated in elements 814A-814D. A total of three minutesof program material remains to be recorded (one minute from each of theprogram segments). These remaining portions are illustrated in FIG. 8Cas 824B-824D. By the time the end of the pre-recorded segment 804 isreached, all of the remaining segments 810A-810D have been recorded. Atthis time, the program material at the end of segment 812 is spliced tothe program material beginning at 814D. Similarly, the program materialat the beginning of each segment 814A-814C is spliced to the end of theprogram material of the preceding program segment. In one embodiment,the program material at the end of the pre-recorded segment 812 isspliced to the program material in the following program segment 814Dbefore the playback of the pre-recorded segment 812 is completed. Sincethe material at the beginning of the following program segment 814D isavailable soon after the viewer begins playing back the pre-recordedsegment, the information required to perform the necessary splicingoperations is available before all of the program material in theprerecorded segment 812 has been played back, and before all of theprogram material of the following segment 814D has been recorded. Hence,the segments may be pre-spliced if necessary.

[0084] In a preferred embodiment of the present invention, the IRD 200includes a single tuner/demodulator 204 and associated circuitry whichcan receive and decode all the necessary channels for VOD service (e.g.channels 3-6 in FIG. 8A) from the same frequency band, and is able tosimultaneously acquire and handle bandwidth from Z program streamswherein Z is defined as:$Z = {{ceiling}\left( \frac{X}{t_{R}} \right)}$

[0085] wherein X is the duration of the program in minutes, and t_(R) isthe amount of pre-cached material in minutes. Hence, in the foregoingexample,$Z = {{{ceiling}\left( \frac{125}{30} \right)} = {{{ceiling}(4.1667)} = 5.}}$

[0086] When one segment is pre-cached, the IRD 200 need only cache theremaining segments. Thus, in this case,$Z = {{{ceiling}\left( \frac{X}{t_{R}} \right)} - 1}$

[0087] If an IRD 200 with a single tuner/demodulator 204 cannotaccommodate the simultaneous reception and storage of Z program streams,then the IRD 200 may not be able to cache the entire program in the timeit takes to play back the initially cached program segment. In thiscase, the single tuner IRD 200 may give precedence to the earliestsegments (e.g. 806D and perhaps 806C) and later record the remaining,yet unrecorded program segments (e.g. segments 806B and 806A).

[0088] Alternate embodiments using IRDs 200 with two or moretuner/demodulators 204 are possible as well. Generally, IRDs 200 withmultiple tuners (n-tuner IRDs 200) can be used to receive staggeredshows on n-frequency bands. For example, the time-staggered videoprograms may be broadcast on two frequency bands, and received by an IRD200 having two tuner/demodulators 204, one tuner/demodulator 204 forreceiving signals on each of the two frequency bands. Further, it ispossible to broadcast m time-staggered video programs on n frequencybands. In this embodiment, IRDs 200 with single tuner/demodulator 204can receive a subset of the m video programs (the time-staggered videoprograms broadcast on one of the n frequency bands), while IRDs 200 withmultiple tuner/demodulators 204 can receive additional video programs aswell.

[0089] Hence, 2-tuner or more (n-tuner) IRDs 200 can be used toeliminate the limitation on the broadcaster for all staggered start timetransmissions of a program to be all on the same frequency.

[0090] N-tuner IRDs 200 can also be used to reduce storage requirementsas well. Since the N-tuner IRD can be used to receive more informationin a given amount of time, the IRD 200 need pre-store much lessinformation, allowing the user to pre-store data for more video programsin the video store 232. For example, an IRD 200 with a singletuner/demodulator 204 can be used to receive the channels 2-6 shown inFIG. 8A. An IRD 200 with two tuner/demodulators 204 can be used toreceive additional material broadcast on a channel 3A (staggered in timefrom channel 3 by 15 minutes), channel 4A (staggered in time fromchannel 4 by 15 minutes), and channel 5A (staggered in time from channel5 by 15 minutes). For such an IRD 200, the rebroadcast interval iseffectively reduced to 15 minutes, and the IRD 200 need only pre-store15 minutes worth of program material (allowing either more pre-cachedprogram material or relaxed storage requirements), instead of the 30minutes of program material required by the single-tuner/demodulator 204RD 200. Advantageously, this additional capability does not render thesingle tuner/demodulator 204 IRD 200 obsolete. As can be seen from theforegoing, additional IRD 200 video store 232 memory permits a reducedrebroadcast interval as well. The foregoing can also be used to downloadand cache the entire program more quickly, thus allowing random programaccess (through fast-forward and reverse operations, for example) morerapidly.

[0091] Several alternatives are available to splice MPEG-coded datatogether. If the splices are infrequent (i.e. at the start of the videoprogram), the data stream can be abruptly switched from the pre-storedvideo program segment 804 to the next subsequent video program segment806D. In this case, the MPEG decoders 214 216 will have to reacquirelock on the program material. This may result in a disruption in theprogram material of at least 1 group of pictures (GOP) in length, whichwould appear similar to a change of channel.

[0092] In another embodiment of the present invention, dual MPEG decoderpairs 214 and 216 (two video MPEG decoders 214 and two audio MPEGdecoders 216) are used. This can be implemented with a transport module208 and MPEG decoder pair 214, 216 for the current segment, and a secondtransport module and second MPEG decoder pair for a next subsequentsegment 806D. When the end of the pre-stored video program segment 804is reached, the video signal from the output of the first MPEG decoder214 is simply switched to the second MPEG decoder, eliminating thedisruption described above. The foregoing can also be implemented with asingle transport module, but dual MPEG decoders 214, 216 as well. Asdescribed above, the length of the pre-stored video program segment canbe increased beyond the rebroadcast interval 604 so that the foregoingsplicing problems can be ameliorated. Similarly, the recording intervalof each of the subsequent video program segments 608 can be increasedbeyond the retransmission interval to promote clean splicing from one ofthe subsequent segments to the next. Another method of MPEG splicinginterleaves or otherwise associates each of the video segments 804, 806with a time code such as the SMPTE standard 312M time code. This timecode can then be used to reassemble and splice together the videosegments 804, 806. The proposed SMPTE standard 312M time code isdescribed in the October 1998 issue of the SMPTE Journal, which ishereby incorporated by reference herein.

[0093] In addition to the foregoing MPEG splicing, there is also theissue of sub-segment management. Sub-segment management addresses thedifficulty posed by the possibility that data packets (e.g. packets402-416) will arrive at the transport module 208 (and hence, thedemultiplexing element 502) in sequence, but in uncertain timeintervals. Each sub-segment, which may comprise one or more packets,must be reassembled to produce the program material.

[0094] Each sub-segment can be assembled by sorting by a channelidentifier (such as the SCID), and the sorting the assembledsub-segments in accordance with a time code. The SMPTE time code, whichis usually defined in terms of hours, minutes, and seconds of theprogram as HH.MM.SS, can be used for this purpose. Alternatively or incombination with the foregoing, a recirculating program time stamp (PTS)value described above can be used for the time stamp. To splice segmentstogether, the last I frame of a previous segment is spliced with thefirst I frame of a subsequent segment. Since the PTS provides anindication of the program time, it can be used to match the I frames sothat the segments may be properly spliced together. Since the PTS is awrap-around binary counter, ambiguities may be encountered. Ifnecessary, a time-of-day clock can be used in conjunction with the PTSto eliminate the ambiguities caused by the wrap-around characteristic.

[0095]FIG. 9 is a flow chart illustrating exemplary program steps usedto select at least one of the plurality of video programs for VODservice. As described earlier herein, the receiver 200 stores a programguide which presents a description of the video programs available forviewing now and for a period of time in the future to the viewer. Eachof the video programs includes a SCID, which identifies that program. Byselecting the SCID, the receiver is set to retrieve the video programsegments associated with the SCID for viewing. An indicator such as aflag, a bit or word can be associated with each video program in theprogram guide for which VOD services are desired. In one embodiment, theindicator may be placed in the program guide by the control center 102before the program guide is downloaded in the receiver 200, eitherthrough the PSTN link 120 or the downlink 118. The program guide is thenscanned 902 to find the VOD service indicator. Video programs associatedwith a VOD service indicator are then identified as programs to berecorded for VOD service, as shown in block 904.

[0096] The indicators may also be placed, removed, or altered by thesubscriber 110 using the keyboard or remote control 224 while viewingthe program guide (essentially scanning through the guide and using anappropriate input to designate the program as a VOD program). In oneembodiment, the video program provider provides baseline VOD servicedesignations, but the user can elect to do so as well, with the user'sselections given priority in the situation where there is inadequatetime and/or bandwidth to pre-store all video segments that have beendefined. It is also possible for a program provider VOD selectiondownload to be interrupted by a user-selected VOD selection, andcompleted when the channels are available to do so. The program guidecan also include information to augment the designation of a program forVOD service. For example, data can be associated with each programindicating when the recording of the pre-stored segment 804 shouldcommence. This allows the video provider to efficiently schedule thestoring of pre-stored segments 804 (using information that may includeglobal knowledge of the VOD selections from each subscriber). Hence, thestorage of pre-stored segments 804 can occur in the middle of the nightor at some other time when there are more channels or more bandwidthavailable to do so. Similarly, if desired, entire movies can betransmitted over multiple channels and made available for true VODservice.

[0097]FIG. 10 is a diagram illustrating another method of selecting oneof the plurality of video programs for VOD service. Here, the subscriberhas not made any express program selections for VOD service, but hasinstead elected to allow the receiver to do so based upon a personalizedindication of which programs the subscriber may want to see. Thispersonalized indication may be obtained from the viewing history of theuser, as sensed and recorded by the receiver 200. Or, the user mayindicate the genre or category of program material that the subscriberprefers. The receiver then uses this information to generate a list ofprograms for which the subscriber will likely want VOD service. The usermay then edit this list to remove uninteresting programs, or simplyallow the receiver to retain those program designations for VOD service.This can be accomplished by accepting a selection of a category of videoprograms for VOD service (e.g. basketball programs, drama, a particularactor or director, designation as including a secondary audio program ina different language), as shown in block 1002. After an appropriatesearch of program information guide information is performed, the VODindictor previously described is associated with each video program thatis a member of the user's category of video programs, as shown in block1004.

[0098] In yet another embodiment of the present invention, the IRD 200is capable of identifying programs that are available for VOD servicewithout the use of a VOD service indicator. This is accomplished byscanning an electronic program guide accessible to or stored within theIRD 200 to determine instances when the same video program is scheduledto be transmitted on multiple channels at staggered starting intervals.This is accomplished by comparing video program information such as theprogram's title and/or other related attributes such as a unique programidentifier for the programs in the program guide. When the program titleof other information match and the scheduled broadcast time arestaggered so as to virtual VOD service, the IRD 200 schedules multiplesimultaneous recordings to record the required program material(typically, the pre-stored segment 804). This capability can beperformed with or without user intervention.

[0099] As described above, the decryption of encrypted data packetsrequires a PIP, which, along with the CWPs, is used by the access card212 to decrypt the data packets and to provide DMA access to thedecrypted data in the system RAM. For non-real time operations, this canbe accomplished in a number of ways.

[0100] In one embodiment of the present invention, the pre-stored videoprogram segment 804 is transmitted and stored in an unencrypted form andthe subsequent video program segments are transmitted and stored in anencrypted form. This allows the subscriber to store and view pre-storedvideo segment 804 for VOD playback without requiring the PIP, and alsoallows the subscriber to view at least a portion of the pre-stored videosegment before requesting the remainder of the video program. Each ofthe subsequent video program segments 806, however require a PIP, andhence, the remainder of the video program cannot be viewed until thereceiver obtains the required PIPs for the remaining segments of thevideo program. These PIPs can be obtained before VOD service begins, orcan be obtained after the commencement of VOD service.

[0101] In one embodiment of the present invention, the retrieval of thepre-stored video program segment 804 can be interrupted (e.g. after 5minutes) and the subscriber 110 queried as to whether they wish topurchase the remainder of the program. If the subscriber 110 so elects,the PIPs can be provided to decrypt and access the remainder of thevideo packets. Since each segment of the video program (806A-806D) isassociated with a different PIP, information at the control center 102can be used to determine which PIPs are required to decrypt the entirevideo program in sequence, and send those PIPs to the subscriber'sreceiver 200.

[0102] In another embodiment of the invention, all of the videosegments, including the pre-stored video segment 804 and the subsequentvideo segments 806 are encrypted. In this case, the PIP for the firstvideo segment must be obtained before the video segment can be decryptedand played back. In one embodiment, the PIP for the first segment isobtained after the subscriber requests VOD service. A message ispresented to the user, giving the price of the VOD program, andconfirming that the subscriber is requesting that service. The controlcenter 102 then makes the PIP for the first video segment available tothe receiver 200 so that the decryption can commence. The control centercan also determine the PIP for the subsequent segments (either alongwith the PIP for the first segment or when the subsequent segments 806are being transmitted), and provide those PIPs to the receiver so thatthe remaining segments can be decrypted.

CONCLUSION

[0103] This concludes the description of the preferred embodiments ofthe present invention. The foregoing description of the preferredembodiment of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form disclosed. Many modificationsand variations are possible in light of the above teaching. For example,a single demultiplexing element (the SCID selection module 502) can beused to demultiplex the information on multiple video channels ofinterest. The foregoing invention can also be implemented with multipledemultplexing elements or with multiple transport modules 208. Forexample, one demultiplexing element and/or transport module 208 can beprovided for each video channel to be received in parallel. Thisconfiguration substantially speeds up the demultiplexing and decryptingoperations. Further, the foregoing operations can also be performed inmultiple transponder embodiments in which the receiver 200 not only hasa demultiplexer element or transport module 208 for each channel, butalso multiple tuners 204, each for receiving a signal on one of aplurality of transponders providing program material via downlink fromthe satellite 108.

[0104] It is also possible to select the length of the pre-storeinterval 804 to be less than the rebroadcast interval 604. In thisembodiment, virtual video on demand service cannot be provided to thesubscriber 110 for any random start time t_(D). However, this method canbe used to improve the near video on demand service (NVOD) toeffectively reduce the rebroadcast interval 604. For example, supposethat the actual rebroadcast interval 604 for the video program materialis 30 minutes. If only 15 minutes of the program is pre-stored, truevideo on demand service for any random start time t_(D) cannot beprovided, since all of the remaining segments cannot be recorded beforethe 15 minute pre-stored interval expires. However, if the subscriber isconstrained to begin replaying the stored material in the last 15minutes of the rebroadcast interval, the pre-stored information can beplayed back while the remainder of the program material segments isstored, without loss of the program material. Hence, the pre-recordedsegment can be used to effectively reduce the latency in the NVODservice by 100%.

[0105] It is intended that the scope of the invention be limited not bythis detailed description, but rather by the claims appended hereto. Theabove specification, examples and data provide a complete description ofthe manufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention resides in the claimshereinafter appended.

What is claimed is:
 1. A method of providing a video program in response to a user demand, wherein the video program is repeatedly transmitted on one of a plurality of channels, each repeated transmission temporally separated from a previous transmission by a retransmission interval and being transmitted on a different channel than the previous transmission, the method comprising the steps of: selecting at least one of a plurality of video programs for VOD service; receiving and storing a first segment of the selected video program in a local storage device before accepting a user demand to view the selected video program, wherein a temporal length of the first segment is substantially equivalent to the retransmission interval; and after accepting the user demand to view the selected video program, retrieving the stored first segment for presentation to the user while receiving and storing subsequent segments of the video program from each of the plurality of channels transmitting a portion of the selected video program in parallel in the local storage device.
 2. The method of claim 1, wherein the step of selecting at least one of the plurality of video programs for VOD service comprises the steps of: scanning a program guide having an entry for each of the video programs for a VOD service indicator; and identifying a video program associated with the VOD service indicator as the selected video program.
 3. The method of claim 2, wherein the program guide is stored in the local storage device.
 4. The method of claim 2, wherein the step of selecting at least one of a plurality of video programs for VOD service comprises the steps of: accepting a selection of at least one of the video programs for VOD service; and associating the VOD indicator with the entry of each video program selected for VOD service.
 5. The method of claim 4, wherein the step of selecting at least one of the plurality of video programs for VOD is performed by the user and the method further comprises the step of presenting a program guide to the user.
 6. The method of claim 2, further comprising the steps of: accepting a selection of a category of video programs for VOD service; and associating the VOD indicator with the entry of each video program that is a member of the selected category of video programs.
 7. The method of claim 1, wherein the step of selecting at least one of the plurality of video programs for VOD service comprises the steps of: scanning a program guide having an entry for each of the video programs to identify at least one video program scheduled to be repeatedly transmitted on one of a plurality of channels, each repeated transmission temporally separated from a previous transmission by a retransmission interval and being transmitted on a different channel than the previous transmission; and selecting the identified video program as the selected video program.
 8. The method of claim 7, wherein the step of scanning the program guide comprises the step of comparing video program information for each of the entries, wherein the video program information comprises a program title.
 9. The method of claim 7, wherein the step of scanning the program guide comprises the step of comparing video program information for each of the entries, wherein the video program information comprises a unique program identifier.
 10. The method of claim 1, wherein the step of storing a first segment of a selected video program in a local storage device comprises the step of receiving data representing the first segment of the video program from a program source in a receiver communicatively coupled to the local storage device at a time scheduled by the program source.
 11. The method of claim 1, further comprising the step of splicing the subsequent segments to the first segment for presentation to the user in response to the user demand.
 12. The method of claim 11, wherein the video segments each comprise a plurality of video sub-segments each sub-segment associated with a time code, and the step of splicing the subsequent segments to the first segment for presentation to the user comprises the step of sorting the sub-segments in accordance with the time codes.
 13. The method of claim 12, wherein the time code is an SMPTE time code.
 14. The method of claim 12, wherein the time code is a program time stamp.
 15. The method of claim 11, wherein the video segments each comprise a plurality of video sub-segments, each sub-segment associated with a time code and a channel identifier, and the step of splicing the subsequent segments to the first segment for presentation to the user comprises the steps of: assembling the sub-segments by the associated channel identifier; and sorting the assembled sub-segments in accordance with the time codes.
 16. The method of claim 1, wherein each of the subsequent segments is encrypted so as to be decryptable with a key before being received and stored in the local storage device, and the method further comprises the steps of: in response to the user demand and while retrieving the stored first segment for presentation to the user, transmitting a message separately identifying each of the subsequent segments of the selected video program and the user to a program source; and receiving the key.
 17. The method of claim 16, further comprising the step of decrypting the encrypted subsequent segments with the keys.
 18. The method of claim 1, wherein each of the segments is encrypted so as to be decryptable by a different key before being received and stored in the local storage device, and the method further comprises the steps of: in response to the user demand, transmitting a message separately identifying each of the segments of the selected video program and the user to a program source; and receiving a key for each of the segments.
 19. The method of claim 18, further comprising the step of decrypting the encrypted segments with each of the plurality of keys.
 20. A method of storing a video program in response to a user demand, wherein the video program is repeatedly transmitted on one of a plurality of channels, each repeated transmission separated in time from a preceding transmission of the video program by a retransmission interval and being transmitted on a different channel than the previous transmission, the method comprising the steps of: selecting at least one of a plurality of video programs; and receiving a plurality of time segments of the selected video program in parallel, wherein each of the time segments is received on a different one of the channels.
 21. The method of claim 20, wherein the time segments of the selected video program are staggered in time by the transmission interval.
 22. The method of claim 20, further comprising the step of: selecting a second video program for real time reception; and receiving the selected second video program in real time while receiving the plurality of time segments of the selected video program in parallel.
 23. The method of claim 20, wherein the step of receiving a plurality of time segments of the selected video program in parallel is performed during a standby interval.
 24. An apparatus for providing a video program in response to a user demand wherein the video program is repeatedly transmitted on one of a plurality of channels, each repeated transmission temporally separated from a previous transmission by a retransmission interval and being transmitted on a different channel than the previous transmission, the apparatus comprising: means for selecting at least one of a plurality of video programs for VOD service; means for receiving and storing a first segment of the selected video program in a local storage device before accepting a user demand to view the selected video program, wherein a temporal length of the first segment is substantially equivalent to the retransmission interval; and means for retrieving the stored first segment for presentation to the user while receiving and storing subsequent segments of the video program from each of the plurality of channels transmitting a portion of the selected video program in parallel after accepting the user demand to view the selected video program.
 25. The apparatus of claim 24, wherein the means for selecting at least one of the plurality of video programs for VOD service comprises: means for scanning a program guide stored in the local storage device having an entry for each of the video programs for a VOD service indicator; and means for identifying the video program associated with the VOD service indicator as the selected video program.
 26. The apparatus of claim 25, wherein the program guide is stored in the local storage device.
 27. The apparatus of claim 25, wherein the means for selecting at least one of a plurality of video programs for VOD service comprises: means for accepting a selection of at least one of the video programs for VOD service; and means for associating the VOD indicator with the entry of each video program selected for VOD service.
 28. The apparatus of claim 26, wherein the plurality of video programs are selected for VOD service by a VOD service provider.
 29. The apparatus of claim 27, wherein the at least one of the plurality of video programs for VOD is selected by the user and the apparatus further comprises means for presenting a program guide to the user.
 30. The apparatus of claim 25, further comprising: means for accepting a selection of a category of video programs for VOD service; and means for associating the VOD indicator with the entry of each video program that is a member of the selected category of video programs.
 31. The apparatus of claim 24, wherein the means for selecting at least one of the plurality of video programs for VOD service comprises: means for scanning a program guide having an entry for each of the video programs to identify at least one video program scheduled to be repeatedly transmitted on one of a plurality of channels, each repeated transmission temporally separated from a previous transmission by a retransmission interval and being transmitted on a different channel than the previous transmission; and means for selecting the identified video program as the selected video program.
 32. The apparatus of claim 31, wherein the means for scanning the program guide comprises means for comparing video program information for each of the entries, wherein the video program information comprises a program title.
 33. The apparatus of claim 31, wherein the means for scanning the program guide comprises means for comparing video program information for each of the entries, wherein the video program information comprises a unique program identifier
 34. The apparatus of claim 24, wherein the means for storing a first segment of a selected video program in a local storage device comprises means for receiving data representing the first segment of the video program from a program source in a receiver communicatively coupled to the local storage device at a time scheduled by the program source.
 35. The apparatus of claim 24, further comprising means for splicing the subsequent segments to the first segment for presentation to the user in response to the user demand.
 36. The apparatus of claim 35, wherein the video segments each comprise a plurality of video sub-segments each sub-segment associated with a time code, and the means for splicing the subsequent segments to the first segment for presentation to the user comprises means for sorting the sub-segments in accordance with the time codes.
 37. The apparatus of claim 36, wherein the time code is the SMPTE time code.
 38. The apparatus of claim 36, wherein the time code is a program time stamp.
 39. The apparatus of claim 35, wherein the video segments each comprise a plurality of video sub-segments, each sub-segment associated with a time code and a channel identifier, and the means for splicing the subsequent segments to the first segment for presentation to the user comprises: means for assembling the sub-segments by the associated channel identifier; and means for sorting the assembled sub-segments in accordance with the time codes.
 40. The apparatus of claim 24, wherein each of the subsequent segments is encrypted so as to be decryptable with a key before being received and stored in the local storage device, and the apparatus further comprises: means for transmitting a message separately identifying each of the subsequent segments of the selected video program and the user to a program source while retrieving the stored first segment for presentation to the user; means for receiving the key; and wherein the message separately identifying each of the subsequent segments of the selected video program and the user to a program source is transmitted in response to a user demand.
 41. The apparatus of claim 40, further comprising means for decrypting the encrypted subsequent segments with the key.
 42. The apparatus of claim 24, wherein each of the segments is encrypted so as to be decryptable by a different key before being received and stored in the local storage device, and the apparatus further comprises: means for transmitting a message separately identifying each of the segments of the selected video program and the user to a program source in response to the user demand; and means for receiving a key for each of the segments.
 43. The apparatus of claim 42, further comprising means for decrypting the encrypted segments with each of the plurality of keys.
 44. An apparatus for storing a video program in response to a user demand, wherein the video program is repeatedly transmitted on one of a plurality of channels, each repeated transmission separated in time from a preceding transmission of the video program by a retransmission interval and being transmitted on a different channel than the previous transmission, the method comprising: means for selecting at least one of a plurality of video programs; and means for receiving a plurality of time segments of the selected video program in parallel, wherein each of the time segments is received on a different one of the channels.
 45. The apparatus of claim 44, wherein the time segments of the selected video program are staggered in time by the transmission interval.
 46. The apparatus of claim 44, further comprising: means for selecting a second video program for real time reception; and means for receiving the selected second video program in real time while receiving the plurality of time segments of the selected video program in parallel.
 47. The apparatus of claim 44, wherein the plurality of time segments of the selected video program in parallel is performed during a standby interval.
 48. An apparatus for providing a video program in response to a user demand, wherein the video program is repeatedly transmitted on one of a plurality of channels, each repeated transmission temporally separated from a previous transmission by a retransmission interval and being transmitted on a different channel than the previous transmission, the apparatus comprising: an input device for accepting a selection of at least one of a plurality of video programs for VOD service; a tuner for receiving multiple segments of the selected video program in parallel, wherein each segment is received on one of the plurality of channels; and a storage device, for pre-storing a first segment of the selected video program, and for storing subsequent segments of the selected video program in parallel while retrieving the pre-stored first segment of the selected video program.
 49. The apparatus of claim 48, further comprising: a memory for storing a program guide having an entry for each of the video programs; and a processor, coupled to the input device and the tuner, and the memory, for scanning the program guide for a VOD service indicator, and for identifying the video program associated with the VOD service indicator as the selected video program.
 50. An apparatus for providing a video program transmitted in segments on a plurality of channels in response to a user demand, comprising: an input device for accepting a selection of at least one of a plurality of video programs for VOD service; a tuner for receiving time segments of the selected video program in parallel, wherein each segment is received on one of the plurality of channels; and a storage device, for storing the segments of the selected video program in parallel wherein each of the time segments is received on a different one of the channels.
 51. The apparatus of claim 50, wherein the time segments of the selected video program are staggered in time by the transmission interval. 